1. Field of the Invention
The present invention relates to equipment and corresponding methods for producing extruded fibers. In particular, the present invention relates to heat control equipment and corresponding methods to control the temperature of molten polymer being extruded to form synthetic fibers.
2. Description of the Related Art
Plural component fiber extrusion processes (e.g., conjugate filament, conjugate staple, conjugate spunbond, and conjugate monofilament) typically employ two or more polymers in combinations and fiber cross-section structure in the production of plural component fibers (e.g., bicomponent, tricomponent, etc.) with selected characteristics. The term “spunbond” refers to a process of forming a non-woven fabric or web from an array of thin, melt-spun polymeric fibers or filaments produced by extruding molten polymer from orifices (the orifices can be, for example, those of a long, generally rectangular spinneret or of a plurality of spinnerets). In a typical spunbond process, one or more molten polymer streams are metered to a heated spin beam that supports a pump block for controlling the flow of molten polymer and a spin pack. The term “spin pack” refers to an assembly for processing and routing the molten polymer to produce extruded polymer streams, including final polymer filtration, distribution systems and a spinneret for extruding molten polymer combinations into plural component fibers.
For certain polymer combinations and/or cross-sections of the fibers to be formed, it is very important to maintain precise temperature control of two or more different polymers so as to control viscosity and/or prevent thermal degradation of the molten polymers as they flow through the spin beam. An exemplary polymer combination that must be precisely temperature controlled, for substantially any fiber cross-section to be formed, is the combination of ethylene-vinyl alcohol copolymer (EVOH) and polyethylene terephthalate (PET). The PET must be extruded above 285° C. while the EVOH will degrade if it is above 240° C. for more than one minute. Typically, the average time that each molecule of the molten polymer remains in a conventional spinning system is well in excess of one minute.
Another example involves the formation of segmented pie fiber cross-sections, where the viscosities of different molten polymers used to form the fiber must be substantially similar to achieve a sharp center point for the extruded fiber. Independent temperature control is often necessary to precisely adjust the viscosity of two or more different polymers to prevent thermal degradation of molten polymer in the spin beam as well as to achieve a desired fiber cross section.
Conventional spunbond and other fiber extrusion processes typically employ a vapor-heated spin beam with a single temperature zone, where the different polymers pass through pipes that are heated by this single zone. The polymers quickly reach the beam temperature due to the vapor heating the pipes. However, such a system does not allow for independent control of the polymer temperatures. As previously noted, this can negatively impact the formation of plural component fibers with different polymer components having different degradation temperatures and/or different viscosity characteristics.
Thus, it is desirable to provide a system that can effectively and independently control molten polymer streams at two or more distinct temperatures during a fiber extrusion process.